The number of British victims killed in a terror attack in the Tunisia beach massacre is expected to rise to at least 30.

A total of 38 people were killed when a gunman opened fire on a beach in the Sousse resort on Friday, with the the Foreign Office already confirming 15 of them were from Britain.

But Foreign Secretary Philip Hammond warned that it was highly likely a "significant number" of victims yet to be identified would be British.

At a briefing following an emergency meeting of Cobra, Home Secretary Theresa May also said the British deaths figure was expected to rise as more information comes out.

The Queen has sent her condolences to the families of those killed, saying the brutal attack had left her and the Duke of Edinburgh "shocked".

The killing spree by Kalashnikov-wielding student Seifeddine Rezgui targeted Western tourists on the beach at the RIU Imperial Marhaba and the RIU Bellevue and only ended when he was shot dead by police. Rezgui was not on any security watchlist in Tunisia.

Three Irish people are also among the dead, including mother-of-two Lorna Carty, from Robinstown, Co Meath.

Yesterday, the family of Larry (56) and Martina Hayes (55), from Athlone, Co Westmeath, told of their devastation after the couple were brutally gunned down as they strolled along the seafront.

It was only a matter of minutes before they were due to leave the coastal town after a week-long sun holiday. It was the third time Mr Hayes, a bus inspector, and his wife of 32 years had holidayed in the area.

The family have been struggling to come to grips with the tragedy, Mr Hayes brother Michael said.

"We're dealing with it the best way we can. Both sides of the family are trying to get through this whole nightmare. It's very tough for everyone," he said.

Larry was described as an ordinary family man who was well-liked by everybody, and his wife as being extremely warm and friendly.

"They had travelled to Tunisia a number of times, and enjoyed everything about the country," said Michael.

The attacker's father and three room-mates were detained and was questioned in the capital, Tunis, an Interior Ministry spokesman said.

The attacker was a 24-year-old graduate of Tunisia's Kairouan University where he had been living with the other students.

"We are sure that others helped, but did not participate," the spokesman said. "They participated indirectly."

Investigators have revealed they are looking for at least one more accomplice, and are sure that Rezgui had help.

A security official confirmed news reports indicating that a swimmer had found the attacker's mobile phone in the Mediterranean.

The phone showed the attacker spoke with his father, Hakim Rezgui, just before his assault. His father said yesterday he was "ashamed" of his son's actions.

Speaking to ITV News soon after being released by police, Mr Rezgui said that when he first heard the news he could not "comprehend" it.

He also said that he was "sorry" for all the lives that had been lost.

Mr Rezgui said: "My God, I am so shocked. I don't know who has contacted him, influenced him or who has put these ideas in his head. He has new friends who got him into this." Authorities believe the suspected accomplices provided the Kalashnikov rifle to Rezgui and helped him get to the scene.

Ballistic tests showed the bullets came from that single weapon, and the attacker was carrying four magazines of ammunition - all were found by investigators, he said.

Shortly after the shooting spree, the spokesman had initially said that two people were involved in the attack before backtracking on that assertion.

The attacker methodically moved from the beach to the hotel's swimming pool, reception and other areas targeting holidaymakers in a massacre that stands as Tunisia's worst terror attack, surpassing the 22 killed in March at the National Bardo Museum outside Tunis - again mostly tourists.